fnResize();
window.onresize = function () {

  fnResize()

};

function fnResize() {

  var deviceWidth = document.documentElement.clientWidth || window.innerWidth

  if (deviceWidth >= 750) {

    deviceWidth = 750

  }

  if (deviceWidth <= 640) {

    deviceWidth = 640

  }

  document.documentElement.style.fontSize = (deviceWidth / 7.5) + 'px'

}
